1. Field of the Invention
This invention relates to the field of pixel display palettes that map a logical pixel value defining pixel appearance to a plurality of physical appearance component values for driving a display device.
2. Description of the Prior Art
It is known within the display systems of computers to provide palettes that map a data word forming a logical pixel value into three physical component values for driving a display device (e.g. a colour monitor). The logical pixel value defines a particular colour which is formed by a combination of three primary colours having particular relative intensities. The primary colours are usually red, green and blue. Each of these primary colours has a component palette associated with it that acts as a look up table addressed via a predetermined set of the bits forming the logical pixel value and outputting a particular component intensity value stored at the particular address accessed within the palette.
It is usual for computers to operate on 1, 2, 4, 8, 16 or 32-bit data words for use as both logical pixel values and their data processing in general. The RAM, long term storage and other systems within the computer are tailored to operate with data words of these lengths.
A problem that arises in such systems is that 8-bit, 16-bit or 32-bit data words are not suited to being partitioned to represent three different primary colour intensities, i.e. these numbers are not divisible by three. Consider the case of each logical pixel value being a 16-bit word. The partitioning of 16-bit logical pixel values has previously been handled in one of two ways.
The first way is that one bit is effectively discarded and five bits are allocated for each colour. This is known as 5-5-5 configuration. The discarding of one bit in every sixteen makes inefficient use of the finite memory and storage resources within the computer system.
The second way is to allocate six bits to one colour and five bits to the other two colours. This technique is referred to as a 6-5-5, 5-6-5 or 5-5-6 configuration (the allocation order being red, green, blue in this nomenclature). A disadvantage of this approach is the lack of flexibility that results from adopting a configuration in which one of the colour components is given twice the number of possible states than the other two colour components.
Another option would be to provide palettes with 2.sup.16 locations and each addressed by the full 16-bit logical pixel values, the partitioning between components being achieved by appropriately loading the palettes with physical appearance component values at the locations indicated by the significant bits of the logical pixel value for that palette. Whilst such an approach gives flexibility, it is impractical to use such large palettes.